Human blood will be inoculated with a well characterized inoculum known to uniformly cause hepatitis in chimpanzees. The infected blood will then be frozen and washed by two different methods and then transfused to four to six chimpanzees. If the chimps do not develop hepatitis suggesting freezing is effective, they will serve as their own controls and the second time receive the same inoculum which has been washed but not frozen. If they still do not get hepatitis, they will then receive the same inoculum in direct transfusion without prior washing or freezing.